1. Field of the Invention
The present invention relates generally to an intelligent channel selection system and method against various interferers in wireless communication systems and, more particularly, to an intelligent channel selection system and method, which generates data for channel selection based on frequency offsets and signal channel power and assigns a channel based on the data for channel selection so as to achieve out-of-band channel selection against various interferers in the industrial, scientific and medical band.
2. Description of the Related Art
A variety of mechanisms capable of solving general coexistence problems in the Industrial, Scientific and Medical (ISM) band have been proposed. In particular, for channel selection methods in the ISM band in which various communication systems supporting various communication standards, in particular, a Wireless Local Area Network (WLAN), Bluetooth and Radio Frequency IDentification (RFID), exist, there are in-band channel selection methods and out-of-band channel selection methods.
The in-band channel selection methods are used to fulfill a desired Packet Error Rate (PER) by reducing the degradation of a signal-to-noise ratio caused by in-band channel interferers, and the out-of-band channel selection methods are used to reduce the degradation of a signal-to-noise ratio caused by out-of-band channel interferers. Furthermore, appropriate channel selection reduces the Minimum Detectable Signal (MDS) of a receiver, thus considerably reducing power consumption through a receiver power control loop and, consequently, increasing the life span of a battery.
For example, in Institute of Electrical and Electronics Engineers (IEEE) 802.15.4 specifications (refer to IEEE Standard 802.15.4-2003 Annex-E pp. 637˜640), there are disclosed in-band channel selection methods, such as Channel Clear Assessment (CCA) and ED/LQI (Energy Detection/Link Quality Indication), and out-of-channel selection methods, such as Dynamic Channel Selection (DCS), Channel Alignment (CA) and Neighbor Pico-net Capability (NPC).
However, in the case where interferers of various sizes exist in the ISM-band in which various communication systems exist, channel selection/assignment should be performed carefully in terms of a minimum detectable signal and power consumption.
For example, the above-described DCS proposed in IEEE 802.15.4 specification is a frequency non-overlapping method, the efficiency of which decreases as the number of interferers increases.
U.S. Unexamined Pat. Publication No. 2003/0181211, which was filed by Razavilar et al., published on Sep. 25, 2003 and entitled “Method and apparatus for dynamic channel selection in wireless modems,” discloses the DCS in which signal channel power is measured based on Received Signal Strength Indication (RSSI), lowest signal channel power is found out and the channel of the lowest signal channel power is assigned. Furthermore, when co-channel signaling exists, channel assigning is performed with the co-channel signaling being taken into consideration.
However, Razavilar el al.'s patent application does not consider the influence of frequency offsets. When neighboring strong interferers exist, the influence of frequency offsets should be considered more than signal channel power, but Razavilar el al.'s patent does not disclose the influence of frequency offsets.
Korean Unexamined Pat. publication No. 2003-0017618, which was filed by Koninklijke Philips Electronics N.V., published on Mar. 3, 2003 and entitled “dynamic frequency selection mechanism for IEEE 802.11 WLAN,” discloses a scheme of selecting a channel based on Clear Channel Assessment (CCA) and RSSI, which does not consider the influence of frequency offsets.
The above-described conventional technologies are dynamic channel selection methods based on RSSI, and have no provision for selecting a channel while considering the influence of frequency offsets as well as RSSI. When a channel is selected using RSSI without the consideration of frequency offsets notwithstanding that frequency offsets have influence greater than that of the signal channel power when strong interferers exist nearby, various defects arise.
In the ISM-band in which various communication systems exist, systems based on different communication standards as well as a system based on a communication standard that a user uses may exist. The biggest problem in such a frequency band is the existence of interferers. Such interferers actually influence CSA at the communication standard that the user uses.
In this case, if inappropriate CSA is performed, a problem arises in that the minimum detectable signal of a receiver and power consumption are increased due to Inter-Modulation Distortion (IMD) and reciprocal mixing effects caused by stronger interferers in surrounding channels.
Accordingly, a method of reducing a minimum detectable signal and power consumption by decreasing the influence of interferers under the same frequency channel environments is required.